Introduction

Split winding transformer is a multi winding power transformer windings of each phase consists of a high voltage winding and a two or a plurality of voltage and capacity are the same. Split transformer normal power transmission only between the high, low voltage winding, and has the short circuit current limiting role in fault.

Several branches of the same capacity, the rated voltage is equal or close to, can be run separately or in parallel operation, can bear the same or different load.When connected to a low voltage winding load or power failure, the low voltage winding is still working normally. No electrical connection between the split winding,magnetic coupling is relatively weak. Split the branch should have a largerimpedance, and division between road and not split winding should have the sameimpedance.

Usually the low voltage winding as the split winding, split into two or three branches,line end marker to lowercase letters and numbers. High voltage winding is notdivided by the two parallel branches, line end sign invariant.

Rated capacity of the total capacity of the division is split winding transformer. Split transformer with two windings is usually called the double split transformer, layout of the low voltage winding spoked (size) to the division and the axial splitting two.

Parameters and equivalent circuit

Several branches in parallel when the split winding into a total of low voltage winding of HV winding operation, called through the operation, the short-circuit impedance of transformer called crossing impedance.

As a branch of a low-pressure winding of HV winding is running, you through theoperation, the short-circuit impedance of transformer called crossing impedancehalf.

When a branch split winding run on another branch, known as the splitting operation, the short-circuit impedance of transformer is called splitting impedance.

Splitting impedance and across the impedance ratio called the splitting coefficients,it is one of the basic parameters of transformer with split winding, generally 3 -- 4.

Three phase double winding double split transformer, and each phase has three windings: not a division of the high voltage winding, it has two branches, but alwaysin parallel, is actually a winding; the same two low voltage split winding. It can be modeled on the three winding transformer, equivalent circuit composed of threeequivalent impedance.

According to the definition of splitting impedance impedance impedance, splitbetween two branches, it is equal to two branches short circuit impedance and,considering the symmetry of the split winding branch arranged, so the branchimpedance equal, equal split impedance 1/2, equal to 1/2 times the splittingcoefficients across the impedance.

Through the impedance is two branch association of impedance voltage windings,and half of that through the impedance is equal to the high voltage winding short circuit impedance and branch of short circuit impedance. So there are:

Short circuit impedance high-voltage winding short-circuit impedance is equal to thebranch through the impedance minus 1/2; and the short circuit impedance branchis equal to 1/2 times the splitting coefficient across the impedance, so the short circuit impedance of HV winding is equal to one minus 1/4 times the splitting coefficient, multiplied in the impedance.

Characteristics and Application

Compared with ordinary transformer, transformer with split windings has the characteristics as follows:

(1) the short circuit current limiting effect. When a branch split winding short circuit,short circuit current passes through semi crossing impedance. Semi crossing impedance equal to the high voltage winding and a branch circuit impedance and,equals one plus 1/4 times the splitting coefficients, multiplied by the crossing impedance. That is to say semi crossing impedance ratio across the impedance of 1/4 split coefficient times across the impedance, which is the common transformershort-circuit impedance is large, so the short circuit current is small.

(2) to improve the self starting condition of motor. Split transformer short-circuit impedance of transformer through impedance than ordinary small, so through thestarting voltage drop to small current, allowing the motor starting capacity.

(3) when a branch split winding short circuit fault occurs, the bus voltage anotherbranch of the drop is small, the residual pressure is high, this is the mainadvantage of split transformer.

The main disadvantage is the high cost of split transformer.

The main application of split transformer two:

(1) when the two generator through a split transformer to the system power supply,splitting splitting transformer effectively increases the impedance between the two generators, so as to reduce the short circuit current objective.

(2) when using a transformer with split into two branches to two independent bus power supply, split between the two bus impedance with high impedance toinfluence each other, reduce bus short-circuit.

Split transformer is usually used as unit above 200MW auxiliary transformer.